Electrodeposition of nickel



ance of the plated article.

United States Patent ELECTRODEPOSITION or NICKEL Bernard P. Martin, Cleveland Heights, Ohio, assignor to The McGean Chemical Company, Cleveland, Ohio, a corporation of Ohio No Drawing. Application December 26, 1957 Serial No. 705,120

Claims. (Cl. 204-49) This invention relates to the electrodeposition of nickel, and to the method of, and materials for, plating base metal objects with nickel in thin deposits of bright, mirror-like finish. More particularly, the invention pertains to a bright nickel plating process, and a bath composition for use therein, in which a high rate of brightening is achieved in extremely thin deposits, even on comparatively rough, unpolished base metal surfaces. Such thin deposits are, moreover, characterized by an exceptional hiding power which imparts to the plated article an appearance of smoothness and luster not obtainable in prior, conventional bright nickel plating processes except by deposits of substantially greater thicknesses.

With the critical shortage of nickel, and its high cost even when available, use of the metal for decorative and protective purposes, primarily of course as a base for chromium plate, must necessarily be restricted, and attempts have been made simply to wash-plate with extremely thin deposits in order to stretch the available supply as far as possible. Such wash deposits have not proved satisfactory, either from the standpoint of providing a suitable protective coating or in respect to appear- Where such thin deposits have been used, the surface of the base metal article has generally first had to be specially bufied or polished. Even when this is done, the resulting plated article lacks the luster and depth of tone which is so highly desired in the finished product.

It is a general object of the invention to produce a thin plate of bright nickel by electrodeposition having an exceptionally rapid, yet excellent, brightening effect and exhibiting enhanced color and appearance in deposits of exceptional thinness. At the same time it is an object of the invention in producing such a bright nickel plate to eliminate a large part, if not most, of the extensive operations previously necessary in preparing the base metal surface prior to bright nickel plating. This is made possible by use of the special plating bath composition disclosed herein under operating conditions which will presently be described in detail.

In line with the foregoing'it is a further object to achieve those results in a manner which requires little or no change in operating practice from that employed heretofore in conventional bright nickel plating processes, the successful operation of which has now become well known to those in the art.

This is accomplished by the addition, to a standard bright nickel plating bath composition of well-known and accepted type, of a supplemental or quick-brightening agent under such conditions that there is no change necessary in plating practice with respect to cathode current density, temperature of operation, pH of the bath, or the normal well-established manner of replenishing the various plating bathconstituents in the course of the process. The deposit thus obtained provides 'a ductile, adherent finish of high brightness and substantially improved hiding power and appearance, comparable to heretofore conventional bright nickel deposits of much greater thickness.

These improvements are obtained by using, in combination with the certain bright nickel bath compositions-hereinafter defined, a supplemental brightener in small but controlled amount, such brightener being certain lignin sulfonic acids or their salts, particularly the alkali metal salts.

It has been proposed generally heretofore to use waste cellulose sulfite liquor and even lignin sulfonic acid as an aid in plating processes. Certain improvements were reported, but disadvantages were also encountered which rendered those proposals impractical and of no commercial utility, at least for bright nickel plating purposes. Among the disadvantages, in the case of nickel plating, is the liability of the deposits to be dull, brittle and nonadherent. These and other disadvantages are obviated in processes carried out in accordance with the invention here disclosed.

It has been standard commercial practice for some time to employ a bright nickel plating bath containing, aside from predominating amounts of the usual nickel salts and boric acid, a primary brightener consisting of an aryl sulfonic acid addition agent as disclosed, for example in Patent Nos. 2,112,818 and 2,114,006 issued to Waite. In

combination with this, a secondary brightener, generally an amino poly aryl methane as disclosed in Patent Nos. 2,198,267 and 2,198,268 granted to Lind et al., is used. The bath contains also an anti-pitting agent, usually a sulfate of a higher aliphatic alcohol, as taught in Patent No. 2,254,161 to Waite and the present inventor. Such a bath is conventional, as indicated, and has served as a standard commercial bright nickel plating bath giving good results.

The present invention is based upon the discovery that certain lignin sulfonic acids and their metal salts, when added in controlled amounts to certain of the standard nickel plating baths mentioned above, will greatly increase the initial rate of brightening of the objects being plated, producing in comparatively thin deposits an appearance which is as good as, if not superior to, deposits of substantially greater thickness produced by conventional bright nickel plating processes known heretofore. EX- cept for the addition in controlled amount of the lignin sulfonate, no other change in the plating solution or the conditions of operation, i. e., bath temperature, acidity or current density, are necessary to obtain the improved results. The deposits are bright, ductile and adherent.

Generally speaking, it now appears that nickel deposits produced in accordance with the invention are equivalent in brightening eifect, as well as hiding power and depth of luster, to a conventional bright nickel deposit approximately two to three times as thick. Accordingly the saving of nickel efiected is readily apparent.

Not all lignin sulfonic acids or lignosulfonates appear to be eifective as addition agents for the foregoing purposes. Lignin itself appears to have no beneficial eifect on the plating bath at all. There is, moreover, considerable variation in eifectiveness among the various ligno-v sulfonates commercially available. This is undoubtedly due to variations in the source of the lignin and the method of extraction. While the chemical properties of a lignosulfonate obtained from a particular pulping process can be maintained to reasonably close standards, the

properties of lignosulfonates obtained from different pulping operations appear to differ considerably. This. is perhaps not surprising in view of the complex chem-' ical structure of lignin. I 7 Typical commercial lignosulfates which areavailable Patented Feb. 3, 1959 as standard products under various trade names include the following:

Trade Name: Producer Maraspersc Marathon Corp., Rothschild, Wis. 'Indulin West Virginia Pulp &'Paper Co.,

Charleston, 8. C. Toranil Lake States Yeast Corp,

Rhinelander, Wis. Protectol General Dyestuffs Corp., New York,

New York Most of these products are sold in different grades, some in powder form, others as a liquid. Particularly suitable among these for the purposes of the invention are Marasperse N, a powder material consisting essentially of sodiumlignosulfonate (approx. 78% on a dry basis), in which the degree of sultonation is 11.3%; "Toranil B," also a powder, consisting essentially of calcium lignosulfonate; Indulin XS-Vz, Indulin XS1 and Indulin XS-2, all powdered sodium lignosulfonates of 5.8%, 10.9%, and 19.7% sulfonation, respectively. Liquid forms include Toranil A a viscous liquid, predominantly calcium lignosulfonate, and Protectol #3 which is said to be a sulfite cellulose liquor extract having about 46% active (lignosulfonate) content. Other grades of the foregoing products, such as Indulin XS-3, 26.9% sulfonated, and XS-4, 32.8% sulfonated, produce improvements in certain respects but these are generally attended by definite disadvantages in other respects, and are not so desirable. For example, while some of the more highly sulfonated Indulins show improvement in ductility of the plate, the brightening capacity is drastically reduced and in some cases appears almost to lead to deposits having even less brightness than the unplated article itself. On the other hand, all of the lignosulfonates found suitable as addition agents are sulfonated to the extent of at least 5%. Marasperse CB, for example, containing 1.69% sulphur, equivalent to 4.3% sulfonated lignin sulfonic acid, is largely ineffective, showing that there is a definite lower limit for achieving the desired result. The etfective range of sulfonation thus extends from about 5% as a minimum to as a desired maximum, although this upper limit does not ap pear nearly so critical as the lower limit.

The amount of lignosulfonate which is added to the bath varies, of course, with the particular type used. In all cases it is small, ranging from about 0.01 to 1.0 gram/liter of bath solution, with an optimum of from 0.01 to 0.5 gram/ liter. For such products as Marasperse N, for example, a particularly effective concentration is about 0.1 to 0.15 gram/liter, and this is generally true of the others mentioned hereinabove.

It is an important condition in the process of the invention that all of the so-called brightening agents that is, the primary brightener, secondary brightener and the quick-brightener (lignosulfonic addition)be used conjointly, as there is a synergistic effect in such use which is not obtained by the use of only one or two of the agents alone.

As a primary brightener for the bath, a number of the aryl sulfo compounds generally used heretofore for this purpose are suitable provided the compound chosen from the known group is unalkylated, otherwise the deposit obtained is brittle and is not satisfactory for most purposes. Examples of primary brighteners in this class which are particularly suitable are the alpha and beta naphthalene monosulfonic acids, the 1,5 and 2,7 naphthalene disulfonic acids and the 1,3,6 naphthalene trisulfonic acids, and salts of the foregoing. Other unalkylated aryl sulfo compounds which may be mentioned include the alpha naphthalene sulfonic acids and sodium o-benzoic sulfimide (saocharin). Other primary brighteners disclosed in the Patent No. 2,112,818 to Waite, mentioned hereinabove, may also serve, so long of course as they are unalkylated compounds.

The amount of aryl 'sulfo primary brightener employed ranges from about 0.5 to 25 grams/liter of bath solution, with'higher concentrations technically possible with such primary agents as naphthalene diand tri-sulfonic acids. The upper limit in such cases is set by economic rather than technical reasons. Generally, from 0.5 to 5.0 grams/ liter give optimum results.

As already mentioned, the secondary brightener employed is an amino poly aryl methane, as described in the aforesaid Patent Nos. 2,198,267 and 2,198,268 to Lind et al. In particular, fuchsin, reduced fuchsin, p,p' methylene dianiline and 2.2',4.4' tetramino 5.5 dimethyl diphenylmethane provide the most satisfactory operation. The amount of such secondary brightener should be at least 2 milligrams/liter of bath solution, and may go as high as milligrams/liter. Preferably, however, the upper limit is on the order of 50 milligrams.

The major constituents of the plating bath are, of course, the inorganic nickel sulfate and chloride salts. Nickel sulfate will, in practice, range from 180 to 400 grams/ liter, and nickel chloride from 8 to grams/liter of bath solution. This corresponds to a total available nickel content of about 40 to 120 grams/liter in solution. An average composition is 280 grains/liter of the nickel sulfate and 60 grams/liter of the nickel chloride, or a total of about 76 grams/liter of available nickel.

Boric acid concentrations of from 8 to 50 grams/liter are desirable as a buffering agent, with a range of 30 to 50 being generally most suitable. Normally about 45 grams/liter of boric acid is considered to give optimum results. An anti-pitter or wetting agent comprising a sulfuric ester of a normal primary aliphatic alcohol having eight to eighteen carbon atoms in the molecule, such as sodium lauryl sulfate, is also desirably included in the bath. Such anti-pitting agents are disclosed in the prior patent to Waite and Martin No. 2,254,161. A small amount of this agent, on the order of 0.1 gram/liter, is suitable.

The pH of the bath may vary from a low of 2.5 to a high of 4.5, determined electrometrically, and the optimum range here is from 3.0 to 4.2. In general the process of the invention involves operating at bath temperatures ranging from about 35 to 60 C, with 50 to 55 C. being especially suitable in commercial practice. Cathode current densities of 25 to amperes per sq. ft. are practical in most cases and 50 to 55 aniperes per sq. ft. is typical of good operating practice.

For purposes of illustration, the following specific examples of plating bath compositions within the scope of the invention are given:

EXAMPLE I Nickel sulfate 280 grams/liter. Nickel chloride 60 grams/liter. Boric acid 45 grams/liter. Naphthalene disulfonic acid 8 grams/liter. Reduced fuchsin 0.005 gram/liter. Sodium lauryl sulfate 0.1 gram/liter. Marasperse N 1 0.01 to 0.1 gram/liter. pH 3.0 (E). Temperature 55 C. Cathode current density 25 to 150 amps/sq. ft.

1 Sodium lignosulfonate.

Using a bath of this composition, excellent electrodepositsof nickel are obtained over the entire range of current densities indicated. At a concentration of 0.1 gram/liter of lignosulfonate, a plated deposit having a thickness of 0.0005 inch has a brightness and tone or luster which is equivalent to that of a deposit 0.001 inch thick plated from a bath of identical composition except for the omission of the lignosulfonate. The rate of brightening when using the'lignosulfonate addition is thus approximately twice that whenit is not present. The biding power of the 0.0005 inch deposit using lignosulfonate is likewise as good as that of the 0.001 inch deposit without the addition. r t

Table I below shows the effect on the important characteristics of the deposit of adding various amount of lignosulfonate.

I Table I [Nickel plate thickness of 0.001 deposited at 50 amps/sq. ft., 55 0.,

g pH=3.0.]

Grams/liter Hiding or Leveling Mara- Brightness Ductility Efi'ect sperse N Taken asstandard soft... gaken tag statndgrd Substantially better titer an S an at 5 ft..." Stillb tte than standard 0%.... Excell nt below standard 126%.... Better than standard.

do 50 Excellent. Substantially below 40 Do.

standard. .60 do 40 Do. .80 Substantially better 35 Do.

than standard. 1 0 do 30 DO.

In considering this tabulation, it is desirable to explain certain terms as they are used therein. In determining the brightness of a nickel deposit, many schemes have been tried to provide scientific means of getting accurate, absolute determinations for comparative purposes. Experience has shown, however, that such comparisons do not necessarily agree at all with what the human eye sees and the latter is, of course, a highly important criterion in the production of suitable brightnickel plated deposits, as it is largely a matter of thepsychological effect produced by what the eye sees which determines in part Whether a particular plated deposit is suitable, assuming other properties such as ductility and adherence are satisfactory. The results obtained from a comparative photometer are often completely misleading for this rea son. Accordingly, the comparisons of brightness or brightening effect given in the foregoing table and referred to hereinafter are based entirely upon the effect upon the eye by visual comparison with a standard or control sample, rather than on any scientifically measured property of the deposit.

In determining ductility, a thin sheet steel test panel or strip is plated to theindicated thickness under the conditions specified. The strip or panel is then bent around a mandrel of small diameter, or even a persons finger, whilelistening carefully for a definite snapping or crying sound characteristic of the rupture of the plated deposit. Usually thede'posit 'will cry long before any visual indication of rupture can be detected in the deposit. If the panel can be bent double (180) without hearing this noise, the deposit is termed soft or ductile. If the panel cries, the angle at which this occurs is measured to provide a comparative basis for indicating ductility. The angles noted in Table I above are such angles.

Hiding or apparent leveling effect, like brightness, as here usedis not quantitatively determined in the absolute sense. There is involved here an appearance of depth, dilfere'ncein color and apparent lack of striations or other surface defects, even though the thickness of the deposit is not as. great as thatof another deposit, and there is not, in fact, as much actual leveling in one case as in another when determined absolutely by a profilometer.

From the foregoing .Table I it will be evident that the brightening effect of .the lignin sulfonate dropsofr rapidly above 0.15 gram/liter until the amount added in solution reaches about 0.8 gram/liter, at which time the brightnes's again picks uptemporarily. .The ductility of the plated deposit, however, falls off sharply with continued increase in amountof lignosulfate addition. It will be apparent that the optimum range runs from about 0.01 to 0.15 gram/liter.

EXAMPLE II A bath of the same composition as Example I is em ployed, except that various technical grades of Indulin XS are employed in place of the Marasperse N. Again, the brightness of the deposit is appreciably greater than that of the contro or conventional bright nickel plate, but in this case the improvement decreases steadily for concentrations of the additive above about 0.4 gram/liter. The lower sulfonated lignins, such as grades XS- /z and XS-1 (representing approximately 5.8% and 10.9% sulfonation, respectively) produce a very definite increase in brittleness of the deposit above about 0.4 gram/liter, while the more highly sulfonated grades (XS2, 19.7%; XS-3, 26.9%; and XS-4, 32.8%) maintain the ductility of the deposit all the way through 1.0 gram/liter, but the brightness of the deposit falls off markedly for concentrations above 0.4 gram/liter. The leveling or hiding power of these more highly sulfonated grades, as well as the lower grades, improves rapidly with additions up to 0.05 gram/ liter but remains fairly constant thereafter with greater concentrations up to about 0.6 gram/ liter, after which this property also declines on further addition of the lignosulfonate. The optimum here accordingly lies within a'range of from around 0.05 to 0.2 gram/ liter of the lower sulfonated Indulins.

EXAMPLE III Again a basic bright nickel bath of the composition shown in Example I was used,except that the lignosul fonate addition here was Toranil. Both Toranil A, a liquid calcium lignosulfonate, and Toranil B, a dried extract of the former, are found to produce an excellent increase in the rate of brightening when added in amounts ranging from about 0.05 to 0.2 gram/liter. Ductility remains good within this range but begins to drop off sharply above about 0.4 gram/liter in the case of Toranil B, and above about 0.6 gram/liter for Toranil A. Hiding power increases steadily withincrease in addition up to around 1.0 gram/liter of Toranil A and to around 0.6 gram/liter of the B product.

EXAMPLE IV Again the same basic bath composition is employed, using in this instance Protectol #3 as the supplementary brightener for quick brightening effect. This is a liquid extract, as mentioned previously, and effective concentrations of this range from 0.01 up to as much as 1.0 gram/liter for quick brightening effects. Brightness, in fact, continues to be good for additions up to at least 3.0 grams/liter, but the leveling effect, which is good up to 2.0 grams/liter, is down at higher concentrations and embrittlement is encountered much above 1.0 gram/liter. Accordingly, the optimum rangehere runs from 0.01 to around 1.0 gram/liter. i

As a specific example of the improvement afforded in the commercial practice of the invention, a conventional bright nickel plating process was employed in plating automotive horn rings and similar components, and it was found necessary to plate for a period of six minutes, resulting in a deposit of about 0.0002" thickness, to obtain a satisfactory finish on the .articles. Using the same bath under the same conditions but adding a lignin sulfonic brightening agent of the type described hereinabove (specifically 0.1 gram/liter of Marasperse N), a finish fully as satisfactory as the other in respect to brightness, appearance of smoothness and luster, was obtained in two minutes. Since the cathode current densities were the same in the two instances, the thickness of deposits are roughly directly proportional to the elapsed times.

As stated hereinabove, mere addition of the effective lignosulfonates alone to a standard Watts type nickel plating bath, without the primary and secondary addition agents mentioned, does not produce the desired result.

. 7 Each of these other bath additions is necessary to get the proper results, although various known compounds within each type or class of additive may of course be used, as indicated. When following this teaching, the brightening effect obtained onthe articles in the course of the plating operation proceeds at a greatly increased initial rate, imparting to the articles in a much shorter time than in conventional bright nickel plating baths a plated deposit which equals the brightness, luster, hiding power and apparent smoothness of prior nickel deposits of much greater thickness. Hence it is now practical to apply a much thinner deposit of nickel for these purposes and eifect large saving in the amount of nickel used.

In the foregoing description and in the claims, the term lignin sulfonic acid as used includes the sulfonates as well, and is further to be understood to refer to the commercial products, such as those listed herein, in which the material is generally available.

This application is a continuation-in-part of my copending application, Serial No. 509,404, filed May 18, 1955, now abandoned.

What is claimed is:

1. An electroplating bath for producing a bright nickel deposit on a base metal, which comprises an aqueous acid nickel electrolyte solution containing a predominating amount of a soluble inorganic nickel salt, said solution further containing, per liter, about 0.5 to 25.0 grams of an unalkylated aryl sulfo compound selected from the group consisting of naphthalene mono-, diand tri-sulfonic acids and saccharin as a primary brightener and about 2 to 100 milligrams of a secondary brightening agent consisting of an amino poly aryl methane from the group consisting of fuchsin, reduced fuchsin, p,p methylene dianiline and 2.2, 4.4 tetramino 5.5 dimethyl diphenylmethane, and a quick-brightening addition agent, said quick-brightening agent being present in amount of from 0.01 to 1.0 gram per liter and being selected from the group consisting of lignin sulfonic acid and its soluble salts wherein the degree of sulfonation is at least about 5%, said bath having a pH of from about 2.5 to 4.5.

2. An electroplating bath for producing on a base metal a plate of bright nickel of improved hiding power andenhanced luster in thin deposits, comprising an aqueous acid electrolyte solution which, in addition to water, consists essentially of a predominating amount of an inorganic nickel salt providing the equivalent of from about 40 to 120 grams per liter of nickel in solution, from about 8 to 50 grams per liter of boric acid, from 0.5 to 25.0 grams per liter of naphthalene disulfonic acid, from 2 to 100 milligrams per liter of reduced fuchsin, approximately 0.1 gram per liter of sodium lauryl sulfate, and from 0.01 to 1.0 gram per liter of a quick-brightening addition agent, said agent being selected from the group consisting of lignin sulfonic acid and its soluble salts wherein the degree of sulfonation is at least 5%, said bath having a pH of from about 2.5 to 4.5.

3. An electroplating bath for plating on a base metal a deposit of nickel having a high rate of brightening in thin deposits, as well as improved hiding power and enhanced luster in such thin deposits in comparision with prior bright nickel deposits, which bath comprises an aqueous acid solution of from 180 to 400 grams per liter of nickel sulfate, 8 to 120 grams per liter of nickel chloride, 30 to 50 grams per literof boric acid, 0.5 to 4.0

grams per liter of naphthalene disulfonic acid, 2 to 50 milligrams per liter of a reduced fuchsin, approximately 0.1 gram per liter of sodium-lauryl sulfate and a supplemental brightening agent in amount of from 0.01 to 1.0 gram per liter, said agent being selected from the group consisting of lignin sulfonic acid and its soluble salts wherein the degree of sulfonation is at least 5%.

4. An electroplating bath as defined in claim 3, wherein said supplemental brightening agent is present in amounts of from 0.01 to 0.5 gram per liter.

5. An electroplating bath as defined in claim 3, wherein 0.1 gram per liter of said supplemental brightening agent is present and said agentis approximately 11% sulfonated.

6. An electroplating bath as defined in claim 3, wherein the degree of sulfonation of said supplemental brightening agent ranges from approximately 5% to 20%.

7. An electroplating bath for deposition of bright nickel in thin deposits of improved brighthening rate, hiding power and appearance, which comprises, per liter of aqueous solution:

in combination with a supplementary brightening agent, in significant amount not less than about 0.01 gram and not exceeding substantially 1.0 gram per liter, selected from the group consisting of lignin sulfonic acid and its alkali metal salts wherein the degree of sulfonation is at least about 5%.

8. The process of producing a ductile bright nickel deposit having a high rate of brightening in thin deposits, as well as improved hiding power and luster in such thin deposits, which comprises electrodepositing nickel from an aqueous acid bath containing the nickel mainly in the form of a soluble inorganic salt, from 0.5 to 25 grams per liter of an unalkylated aryl sulfo compound selected from the group consisting of naphthalene mono-,

di-, tri-sulfonic acids and saccharin as a primary brightener, from 2 to milligrams per liter of a secondary brightening agent consisting of any amino poly aryl methane selected from the group consisting of fuchsin,

reduced fuchsin, p,p' methylene dianiline and 2.2, 4.4

tetramino 5.5 dimethyl diphenylmethane and a quickbrightening agent consisting of an amino poly aryl being present in amount of from 0.01 to 1.0 gram per liter of bath solution and being selected from the group consisting of lignin sulfonic acid and its soluble salts wherein the degree of sulfonation is at least about 5%, said bath having a pH of from 2.5 to 4.5, said process being carried out at a bath temperature of from 30 to 60 C., and at a cathode current density of from 25 to amperes per square foot.

9. The process as defined in claim 8, wherein said bath also contains a small amount, on the order of 0.01 gram per liter, of an anti-pitting agent comprising a sulfuric ester of a normal primary aliphatic alcohol having from eight to eighteen carbon atoms in the molecule, and from 8 to 50 grams per liter of boric acid as a buffering agent.

10. The process as defined in claim 8, wherein the amount of lignin sulfonic addition agent ranges from 0.01 to 0.5 gram per liter of solution.

11. The process as defined in claim 8, wherein the lignin sulfonic addition agent is sulfonated from at least 5% to about 20% of its maximum degree of sulfonation.

12. The process of producing a ductile bright nickel deposit having a high rate of brightening in thin deposits, as well as improved hiding power and enhanced luster in such thin deposits in comparison with prior bright nickel deposits, which comprises electrodepositing nickel rom an aqueous acid bath containing, perliter of solution, from to 400 grams of nickel sulfate, 8 to 120 grams of nickel chloride, 30 to 50 grams of boric acid, 0.5 to 5.0 grams of naphthalene disulfonic acid, 2 to 50 milligrams of reduced fuchsin, approximately 0.1 gram of sodium lauryl sulfate, and a supplemental brightening agent in amount of from 0.01 to 1.0 gram, said agent being selected from the group consisting of lignin sulfonic acid and its soluble salts wherein the degree of sulfonation is at least 5%, said bath having a pH of from 3.0 to 4.2 and said process being operated at a bath temperature of 50 to 55 C. with a cathode current density of 50 to 55 amperes per square foot.

13. The process as defined in claim 12, wherein the amount of lignin sulfonic addition agent ranges from 0.01 to 0.5 gram per liter of solution.

14. The process as defined in claim 12, wherein 0.1 gram per liter of said lignin sulfonic addition agent is present and said agent is approximately 11% sulfonated.

15. The process of producing a ductile bright nickel deposit having a high rate of brightening in thin deposits, as Well as improved hiding power and enhanced appearance in such thin deposits, which comprises electrodepositing nickel from an acid bath containing, per liter of solution:

in combination with a supplementary brightening agent, in significant amount not less than about 0.01 gram per liter of bath solution and not exceeding substantially 1.0 gram per liter, selected from the group consisting of lignin sulfonic acid and its alkali metal salts wherein the degree of sulfonation is at least about 5%.

References Cited in the file of this patent UNITED STATES PATENTS Lind et a1 Apr. 23, 1940 Hull et a1 Feb. 23, 1943 UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,872,392 February 3, 1959 Bernard P. Martin It is hereby certified that error appears in the -printed specification of the above numbered. patent requiring correction and that the said Letters Patent should read as corrected below.

Column 8, line 9, for "brighthening" read brightening line 38, for "any amino" read an amino line 42, for "brightening agent consisting of an amino poly aryl read brightening addition agent, said quick-brightening agent Signed and sealed this 9th day of June 1959.

(SEAL) Attest:

KARL H; AXLINE ROBERT c. WATSON Attesting Officer Commissioner of Patents 

1. AN ELECTROPLATING BATH FOR PRODUCING A BRIGHT NICKEL DEPOSIT ON A BASE METAL, WHICH COMPRISES AN AQUEOUS ACID NICKEL ELECTROLYTE SOLUTION CONTAINING A PREDOMINATIONG AMOUNT OF SOLUBLE INORGANIC NICKEL SALT, SAID SOLUTION FURTHER CONTAINIG, PER LITER, ABOUT 0.5 TO 25.0 GRAMS OF AN UNALKYLATED ARYL SULFO COMPOUND SELECTED FROM THE GROUP CONSISTING OF NAPHTHALENE MONO-, DI- AND TRI-SULFONIC ACIDS AND SACCHARIN AS A PRIMARY BRGHTENER AND ABOUT 2 TO 100 MILLIGRAMS OF A SECONDARY BRIGHTENING AGENT CONSISTING OF AN AMINO POLY ARYL METHANE FROM THE GROUP CONSISTING OF FUCHSIN, P,P'' METHYLENE DIANILINE AND 2.2'', 4.4'' TETRAMINO 5.5'' DIMETHYL DIPHENYLETHANE, AND A QUICK-BRIGTENING ADDITION AGENT, SAID QUICK-BRIGHTENING AGENT BEING PRSENT IN AMOUNT OF FROM 0.01 TO 1.0 GRAM PER LITRE AND BEING SELECTED FROM THE GROUP CONSISTING OF LIGNIN SULFONIC ACID AND ITS SOLUBLE SALTS WHEREIN DEGREE OF SULFONATION IS AT LEAST ABOUT 5%, SAID BATH HAVING A PH OF FROM ABOUT 2.5 TO 4.5. 